They're nothing new, however, according to activists who warn that the tactics, along with recent deaths involving police in other cities, are indicative of a troubling trend among law enforcement agencies.

“Anyone who studies American history [will find] that there has always been a national problem between law enforcement and its abusive tactics against people of color generally and poor people in particular,” said al-Hajj Talib Abdur-Rashid, president of the Islamic Leadership Council of Metropolitan New York.

The killing of the 18-year-old Michael Brown by a Ferguson police officer last Saturday sparked the riots that gripped the St. Louis suburb on and off all week.

They came just weeks after furor erupted in New York, when a plainclothes officer used a "chokehold" in an arrest of a man allegedly selling untaxed cigarettes. The man later died, a death the city coroner ruled was a homicide.

The deaths are indicative of a crisis of trust between law enforcement and civilians, and it’s nothing new, Abdur-Rashid said.

"Law enforcement still hasn’t gotten it right,” he said.

'Broken Windows' Theory

In recent decades, police agencies have employed a theory of community policing known as “broken windows.” The theory says that police must show zero tolerance for smaller crimes, because they will lead to larger crimes if left unchecked.

Critics of "broken windows" policing say it has led to overzealousness by police. Officers end up arresting civilians for minor infractions such as littering, playing music too loudly or drinking beer in public, rather than just warning them.

New York City police officers also have a quota for arrests, said Robert Ganji, director of the Police Reform Organizing Project.

“And what cops do under the quota system is arrest people because they don’t get credit for issuing a warning and having that take care of the problem," he said. "They don’t get credit if they break up a fight between two boys and send them home. They only get credit if they arrest two boys for assault.”

Job pressure and fear can lead some police to regard people in higher crime and minority neighborhoods as potential troublemakers, not innocent citizens, Ganji said. That attitude makes for deep resentment within the community, bad morale for the police and lately, criticism by the general public, he said.

Ganji said police he’s spoken with “say things like ‘I really don’t like this. I took this job because I want to help people. But if I focus on helping people, they’ll hang me.’"

Ambivalence

For people to complain when police use force, while appreciating the benefits a police force has brought them is hypocritical, argued Maki Haberfeld, a former officer who chairs the Department of Law and Police Science at the John Jay College of Criminal Justice in New York.

"They’re not there to punish people who violate the law. But we do need to take it within the context that police officers interact with people who are violent, [and] have violent pasts,” she said.

Police make errors of judgment, sometimes fatal ones, she said. There, the blame lies with the lack of mandatory national training standards for police on when and how to use force appropriately.

That’s a systemic failure, not a failure by individual police officers or police departments, Haberfield argued.

“They don’t receive the right tools to police the way they are supposed to police,” she said.

Experts cite other contributing factors: poverty, a lack of education, few jobs or economic opportunity.